1. Field of the Invention
The present invention relates to a method and apparatus for determining ovulation state and predicting ovulation in females and particularly to a non-invasive method and apparatus for determining the onset of hormonal changes in humans based on detection of changes in psycho-acoustic response of the human body to sound.
2. Prior Art
Some physiological changes in humans are preceded by a sudden increase in the level of certain hormones. One such change, the onset of ovulation in women, is preceded by a sudden increase in the level of luteinizing hormone (LH) in the blood stream. This LH concentration increase, or surge, begins approximately 36 hours to 48 hours preceding ovulation, peaks about 18 hours prior to ovulation and ends at the time of ovulation. The surge primarily results in expulsion of the egg from the ovum after the receptors of the ovaries become affected by the increased concentration of LH. The increased levels of LH, and other accompanying hormonal changes, cause several physiological and psychological changes to occur. The term "psycho-acoustic" is used herein to refer to these changes, i.e., changes which do not appear to be related to physical changes in the ear, but appear to be related to the way sound is sensed by the central nervous system. The term "ovulation state" is used herein to refer to the present physiological and psycho-acoustic state of a woman in relation to the time ovulation will occur in her. The term "pre-ovulatory" is used to refer to that ovulation state which exists during the time period beginning 36 to 48 hours prior to ovulation and ends around the time of ovulation. The term "non pre-ovulatory" refers to the time period which falls outside the pre-ovulatory time period.
Different methods of indication of changes in female physiological characteristics before and during her menstrual cycle are currently used in clinics to determine the onset of the ovulation. For example, increased concentrations of LH can be detected in a woman's urine during the LH surge. Other physiological changes in a woman, such as basal body temperature, changes in vaginal mucus secretions and cervical surface texture, also occur near the time of the ovulation. Reliance on these natural indicators of ovulation is subjective and often requires extensive training to assess. Moreover, urine and blood-based ovulation tests are primarily performed in clinics, even though some home urine test kits are available on the market. Currently, to perform the most reliable ovulation test--an LH level increase measurement--a clinical analysis of venous blood is required. This procedure is expensive, since a blood sample must be processed in a laboratory and assistance of a trained clinician is usually necessary.
Furthermore, because of the delays associated with lab testing, the predictive fertile window (the 5-day period preceding ovulation) is greatly reduced, which, in turn, reduces the probability of impregnation. Additionally, the LH surge detection in blood or urine often requires multiple tests. At-home urine test kits are quite expensive, priced from $20 per package, and contain only 5 test strips per kit. In addition, there are other disadvantages associated with at-home urine testing due to a large number of factors that alter the test's accuracy. Being the blood's filtrate, urine contains elevated LH concentrations during the pre-ovulatory surge; these concentrations can be detected using a urine analysis. However, such at-home urine testing is not entirely dependable, because the test results are reliable only when conducted at certain times of the day. For example, the first urine in the morning can not be reliably analyzed, as the LH concentration within it is altered, skewing test results. Additionally, it can take up to 12 hours after the LH surge in the blood for detectable levels of the hormone to collect in the urine, thus reducing the predictive fertility window. Another disadvantage of at-home urine tests lies in their inability to adjust the scale per specific physiological parameters of an individual. Furthermore, the test results are affected by pharmaceuticals and common chemicals like soap. Finally, detection of an LH surge usually requires multiple testing which increases costs.
Invasive methods of ovulation detection, such as, for example, radioimmunoassay, require a homogenized blood serum. However, since radioimmunoassay measures both beta subunits and LH, it is not an entirely reliable LH indicator. A radioreceptor assay method measures only LH-blood serum concentrations and produces more reliable results. Nevertheless, the assay required either a homogenized blood or urine serum for testing, thus, decreasing the predictive fertile window because of the delay lab testing requires.
Therefore, because of the number of unreliable factors, conditions and expenses associated with clinical, serum, or at-home urine testing, a more reliable, easy to operate ovulation indicator used at the convenience of an individual will be beneficial in fertility assessment.
It is known that two significant psycho-acoustic changes take place in correlation with a woman's ovulation cycle. It has been documented that sound perception inside the ear occurs by two different means of audio interpretation, namely, monaural and binaural beat interpretation. Monaural interpretation occurs when an individual hears a tone at the same frequency in both ears and perceives the vibrations as sound. Usually an individual can detect sounds in the frequency range between 20 and 20 000 Hz. Binaural audio interpretation occurs when two tones of frequencies differing by 3-6 Hz sound in different ears. Under normal conditions an individual utilizes central summation to combine the two tones and perceive the resulting sound as the average of the two different frequencies. This phenomenon produces a warbling effect and is perceived as a roving sound throughout the head.
Hearing sensitivity changes, i.e., changes in hearing threshold, to sounds in certain frequency ranges have been observed to correlate with the preovulatory state. During the LH surge a female loses 30-35 dB of hearing and becomes less sensitive or unable to perceive as many frequencies as she would normally perceive. However, her range of sound interpretation shifts, so she becomes capable of interpreting a greater number of tones at lower frequencies, typically tones in the range of about 6 000 Hz to about 14 000 Hz.
It has been discovered that a change in monaural and binaural perception occurs in females during the preovulatory period. For example, just before ovulation and menstruation females experienced a significant decrease in their abilities to measure absolute pitch.
In order to be detected by a woman during the onset of ovulation (the pre-ovulatory state), the volume, or intensity of sounds in the general range of about 6 000 Hz to about 14 000 Hz must be increased by about 10 dB to about 40 dB above the volume, or intensity at which she can detect these sounds at other times during her ovulation cycle. Therefore, by detecting and measuring this change in hearing sensitivity the ovulation state of the woman can be determined, and the time of ovulation predicted.
Loss of the ability to synthesize binaural beats is another psycho-acoustic change which has been observed to correlate to the preovulatory state. It has been discovered that the female loses the ability to discern warbling effect within certain frequency ranges during the 24-hour period before ovulation during the LH cycle. The usual form of binaural hearing occurs when two tones differing by about 3 to 6 Hz are presented to the human ear, one tone to each ear. For example, if a tone of 600 Hz is presented to one ear and a tone of 603 Hz is presented to the other ear, the central nervous system synthesizes a warbling tone.
The psycho-acoustic phenomenon of binaural beat synthesis is most noticeable at beat frequencies below 1000 Hz and the phenomenon becomes quite distinct in the frequency range of about 400 Hz to 800 Hz. By sensing the presence and, subsequently, the loss of this ability to hear the warbling sound, the onset of the increase in LH and other accompanying hormonal changes preceding ovulation can be detected and the probable time of ovulation predicted.
Knowledge of her ovulation state can be used by the woman for birth control purposes, i.e., to increase or decrease the probability of conception. There has been a long felt need for an effective, non-invasive method and means for determining ovulation state and predicting the time of ovulation.